John,
I spent a fair amount of time last night reflecting on this situation. I am coming up blank. If it was the trans, it would seem to me that it would still do it even with the driveshaft off it. The other possibility would be the yoke in the rear bushing, BUT you would have really struggled getting the yoke out of the trans. As I said on the phone, even thought the trans is way out of warranty, I will be happy to look at it for you to try to determine if there is an issue in it. Keep me posted.
Thanks,
Jamie